From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f72.google.com (mail-ed1-f72.google.com [209.85.208.72]) by kanga.kvack.org (Postfix) with ESMTP id 886086B0006 for ; Mon, 30 Jul 2018 08:05:36 -0400 (EDT) Received: by mail-ed1-f72.google.com with SMTP id h26-v6so55278eds.14 for ; Mon, 30 Jul 2018 05:05:36 -0700 (PDT) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id l6-v6si3438926edc.305.2018.07.30.05.05.34 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 30 Jul 2018 05:05:35 -0700 (PDT) Date: Mon, 30 Jul 2018 14:05:29 +0200 From: Michal Hocko Subject: Re: [PATCH v1] mm: inititalize struct pages when adding a section Message-ID: <20180730120529.GN24267@dhcp22.suse.cz> References: <20180727165454.27292-1-david@redhat.com> <20180730113029.GM24267@dhcp22.suse.cz> <6cc416e7-522c-a67e-2706-f37aadff084f@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <6cc416e7-522c-a67e-2706-f37aadff084f@redhat.com> Sender: owner-linux-mm@kvack.org List-ID: To: David Hildenbrand Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Greg Kroah-Hartman , Ingo Molnar , Pavel Tatashin , Andrew Morton , Dan Williams , Jan Kara , Matthew Wilcox , =?iso-8859-1?B?Suly9G1l?= Glisse , Souptick Joarder , "Kirill A. Shutemov" , Vlastimil Babka , Oscar Salvador , YASUAKI ISHIMATSU , Mathieu Malaterre , Mel Gorman , Joonsoo Kim On Mon 30-07-18 13:53:06, David Hildenbrand wrote: > On 30.07.2018 13:30, Michal Hocko wrote: > > On Fri 27-07-18 18:54:54, David Hildenbrand wrote: > >> Right now, struct pages are inititalized when memory is onlined, not > >> when it is added (since commit d0dc12e86b31 ("mm/memory_hotplug: optimize > >> memory hotplug")). > >> > >> remove_memory() will call arch_remove_memory(). Here, we usually access > >> the struct page to get the zone of the pages. > >> > >> So effectively, we access stale struct pages in case we remove memory that > >> was never onlined. So let's simply inititalize them earlier, when the > >> memory is added. We only have to take care of updating the zone once we > >> know it. We can use a dummy zone for that purpose. > > > > I have considered something like this when I was reworking memory > > hotplug to not associate struct pages with zone before onlining and I > > considered this to be rather fragile. I would really not like to get > > back to that again if possible. > > > >> So effectively, all pages will already be initialized and set to > >> reserved after memory was added but before it was onlined (and even the > >> memblock is added). We only inititalize pages once, to not degrade > >> performance. > > > > To be honest, I would rather see d0dc12e86b31 reverted. It is late in > > the release cycle and if the patch is buggy then it should be reverted > > rather than worked around. I found the optimization not really > > convincing back then and this is still the case TBH. > > > > If I am not wrong, that's already broken in 4.17, no? What about that? Ohh, I thought this was merged in 4.18. $ git describe --contains d0dc12e86b31 --match="v*" v4.17-rc1~99^2~44 proves me wrong. This means that the fix is not so urgent as I thought. If you can figure out a reasonable fix then it should be preferable to the revert. Fake zone sounds too hackish to me though. -- Michal Hocko SUSE Labs